Ballast apparatus for starting and operating electric discharge lamps



y 4, 1963 F A. NEUSBAUM 3,089,980

BALLAST APPARATUS FOR STARTING AND OPERATING ELECTRIC DISCHARGE LAMPSFiled June 1, 1961 2 Sheets-Sheet 1 May 14, 1963 F. A. NEUSBAUM3,089,980

BALLAST APPARATUS FOR STARTING AND OPERATING ELECTRIC DISCHARGE LAMPS 2Sheets-Sheet 2 Filed June 1, 1961 [/7 149/? 5'0): Framz A. A/eusaum,

United States Patent 3,089,980 BALLAST APPARATUS FOR STARTING AND()PERATING ELECTRIC DISCHARGE LAMPS Frank A. Neusbauni, Danville, Ill,assignor to General Electric Company, a corporation of New York FiledJune 1, 11961, Ser. No. 114,063 llti (Ilairns. (Cl. 315-97) Thisinvention relates to ballast apparatus for starting and operatingelectric discharge lamps and more particularly to such a ballastapparatus for starting and operating gaseous discharge lamps such asfluorescent lamps employing an auxiliary starting aid circuitarrangement.

In most fluorescent lamp lighting applications, the ballast apparatusfor the lamp is mounted within the lamp fixture. Each fluorescent lampis positioned in a predetermined spaced relationship with the fixture sothat a capacitive effect is produced between the lamp and the fixture.Although a grounded conductive strip such as a narrow ribbon of silvergraphite deposited on the lamp bulb may be used in the same manner as alamp fixture, the fixture itself is generally used as a starting aid forthe lamp because it is a relatively inexpensive and simple arrangement.

The effect of grounding the fixture or conductive plate and groundingone side of the low potential side of the ballast circuit is to placethe lamp fixture in electrical connection with the lova potential sideof the ballast circuit. Further, it will be understood that if the lowpotential side of the distribution line is grounded as is the case in anormally grounded distribution system and if the ballast case andfixture are grounded, no auxiliary starting aid device will be needed inautotransformer connected ballast circuits. In the event thedistribution system is not effectively grounded, or in the event thatthe lamp fixture is not grounded, a starting aid resistor is provided sothat the low potential side of the ballast circuit is in electricalconnection with the fixture and the auxiliary starting aid circuit formsa complete loop. The impedance provided by the resistor prevents alethal current flow to the ballast case. Ballast circuits which utilizeisolated primary designs must use some auxiliary means to return one endof the secondary circuit to the ballast enclosure, regardless of whetherthe primary distribution system is grounded.

The auxiliary starting aid circuit or loop is completed through groundfrom the conducting fixture to the low potential side of the primarywinding of the ballast transformer. The low potential side of theprimary is usually grounded through a resistor to the ballast case.Since the ballast case is generally connected to the lamp fixture, thefixture is thereby connected in electrical circuit with the lowpotential side of the primary winding. Because of the high impedance ofthe grounding resistor and of the capacitive coupling between the lampand fixture, only a small amount of current will fiow in the startingaid circuit from the electrode to the fixture. However, this current issufiicient to increase substantially the ionization of the gas in thevicinity of the lamp electrode. The increased ionization potential inthe vicinity of the lamp electrodes permits the lamp to be started withlower starting voltages applied across the lamp terminals. The startingvoltage at the output terminals of the ballast transformer isconcurrently placed across the electrodes of the lamp with the startingaid potential until the lamp is ignited. Once the lamp has ignited, thestarting aid circuit is substantially ineffective in the circuit becauseof the high impedance of the capacitive coupling between the lamp andfixture.

It is desirable that a ballast apparatus be provided wherein thestarting aid circuit will provide a suflicient 3,089,980 Patented May14, 1963 ionization potential voltage so that the ballast apparatus canbe operated from a grounded or ungrounded power supply in conjunctionwith a grounded or ungrounded fixture. For these various grounded andungrounded conditions of operation which are not infrequentlyencountered in practice, the starting aid resistor has not been entirelysatisfactory. For example, in an installation where the primary windingof the ballast transformer is connected to an ungrounded power supplyand the ballast case is ungrounded, the starting aid potential wasactually decreased by an auxiliary starting aid circuit utilizing aresistor connected between the low potential end of the primary and theballast case. Thus, in such an installation the starting resistor has adetrimental effect on starting. Further, the starting aid resistor is anadditional component of the starting aid circuit and adds to the cost ofthe ballast apparatus. From a standpoint of economy, it is, of course,desirable to reduce the number of components used in any electricalcircuit.

Accordingly, it is a general object of my invention to provide a new andimproved auxiliary starting aid arrangement for a ballast apparatus foroperating one or more gaseous discharge lamps.

Another object of my invention is to provide an improved auxiliarystarting aid circuit arrangement in a ballast apparatus wherein the needfor an auxiliary starting aid resistor is eliminated.

A further object of my invention is to provide a new and improvedauxiliary starting aid circuit arrangement in a ballast apparatuswherein an increased starting aid potential is provided when the ballastcircuit is operated from a grounded and ungrounded power supply.

Briefly stated, in accordance with one aspect of my invention, I haveprovided a ballast apparatus having a high leakage reactance transformerand a power factor capacitor connected in circuit with the secondarywinding thereof. The capacitor container is connected to ground and thereactive impedance developed between the capacitor container and thecapacitor outer foil is utilized in an auxiliary starting aid circuit.The lamp or lamps energized by the ballast apparatus are positioned inclose proximity to a conducting fixture and disposed in capacitiverelationship therewith. The auxiliary starting aid circuit applies atleast the voltage developed across the secondary winding across the lampelectrode and the fixture capacitively coupled therewith. The groundedconnection to the capacitor container solely provides a return path forthe auxiliary starting aid current to the ballast apparatus. When thelamp is started, the reactive impedance between the capacitor case andthe capacitor outer foil is sufficient to prevent any significant amountof current flow out of the ballast circuit.

The subject matter which I regard as my invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. My invention, however, both as to organization and modeof operation, together with further objects and advantages thereof, maybe best understood by reference to the following description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram ballast apparatus incorporating thefeatures of the present invention;

FIG. 2 is a plan view of the ballast apparatus shown schematically inFIG. 1 in which the circuit connections have been omitted;

FIG. 3 is a schematic diagram of an improved ballast apparatus foroperating a pair of serially connected discharge lamps in accordancewith the invention;

FIG. 4 is a plan view of the ballast apparatus shown schematically inFIG. 3 wherein the circuit connections have been omitted; and

FIG. 5 is a view partly in section of a power factor capacitor such asis conventionally employed in a ballast apparatus with the capacitorassembly partially-unrolled.

Referring now to the drawings and more specifically to FIG. 1, aschematic circuit diagram of one form of applicants invention foroperating a hot cathode type of fluorescent lamp L is shown. A ballastapparatus is contained within a ballast case 11 represented by dashedlines. The ballast apparatus 113 includes a high reactance transformer12, a power factor capacitor 15 having a metallic or conductivecontainer 9, and output leads 14, 15 connected to cathodes 16, 17 oflamp L. A grounded conductive plate is identified generally in FIG. 1 byreference numeral 18 and in most applications is the lighting fixture.Lamp L is positioned in proximity to the conductive plate 18 so as to beicapacitively coupled therewith. A spacing of approximately /8 of aninch may be employed between the lamp L and the conductive plate 18.

The high reactance ballast transformer 12 includes a magnetic core 19, aprimary winding P, a secondary winding S, cathode heating windings H H amagnetic shunt 20 and input terminal leads 21, 22. As shown in FIG. 2,the primary winding P and the secondary winding 5 are placed side byside on a central winding leg 23 of the mag netic core 19 and areseparated by magnetic shunts 20. It will be appreciated that the leakagereactance of the ballast transformer 12 may be readily increased by theinclusion of a high reluctance leakage path or shunts of magneticmaterial between the primary winding P and the secondary winding S. Inthe exemplification of the invention shown in FIGS. 1 and 2, the fluxleakage path is formed of inserted shunts 20. A high leakage reactancetransformer is normally required in ballast circuits in order that thecurrent How in the lamp circuit be limited because the discharge lamp Lhas a negative resistance characteristic. It will be understood thatflux leakage paths may be formed either through nonmagnetic material,such as air, or through magnetic material by the provision of projectingshunt legs integrally formed with the yoke sections or insertable shunts21) as are employed the illustrative embodiment of the invention.

Referring again to FIG. 2, it will be seen that magnetic core 19 has acentral winding leg 23 and yoke sections 24, 25 which are firmly held inassembled relation with the central leg 23 by the clamping elements 26,27. Primary winding P and cathode heating windings H H are included incoil assembly 28. Coil assembly 29 which includes the secondary windingS is disposed on the central winding leg 23 alongside of and spaced fromcoil assembly 2S.

Ballast apparatus 1% is housed in an elongated conductive ballast case11 which is covered with a cover plate 30, only portions of which areshown. The capacitor 13 and container 9 are disposed at the other end ofthe ballast case 11 and container 9 is connected to the ballast case 11by lead 31. As shown in FIG. 2, one end of the lead 31 is attached tothe capacitor container 9 by some suitable attaching means such assolder and at the other end it is attached to an eyelet portion 32. Whenthe cover plate 30 is assembled with ballast case 11, the lead 31 isengaged between eyelet portion 32 and the cover plate 30. Since theballast case 11 is generally secured to a lamp fixture, which is shownschematically in the circuit diagram of PEG. 1, as the conductive plate18 connected to a ground 33, the ballast case is also substantially atground potential as shown by the connection of ballast case 11 to groundin FIG. 1.

As shown in FIG. 1, the capacitor container 9 is representedschematically by the dashed rectangle 9 and is connected by lead 31 tothe ballast case 11. The reactive impedance developed between thecapacitor container 9 and the capacitor outer foil of capacitor 13 isrepresented schematically in FIG. 1 by a capacitor 35 and connections36, 37 shown in dashed lines. In effect, by connecting the capacitorcontainer 9 to the grounded ballast case 11 or any other suitableground, I have discovered that such an arrangement is equivalent toconnecting one end of the secondary winding S in series circuit with oneplate of the capacitor 35, the other plate of which is connected toground. Thus, one end of the secondary winding S is grounded through acapacitor by connecting the container 9 of capacitor 13 in electricalcircuit with ballast case 11, and the capacitive impedance in tr ecircuit is isufficient to prevent any appreciable current flow from theballast apparatus 10 to ground. Capacitor 13 has sufficient capacitivereactance as compared with the inductive reactance of a ballasttransformer 12 to draw a leading current through the secondary windingS. A bleeder resistor R may be connected across capacitor 13, ifdesired.

As shown in FIG. 1, the primary winding P has a pair of input terminalleads 21, 22 for connection to a suitable alternating current supplyline shown schematically by the dashed lines 39, 4'19, the low potentialside being shown by the supply line at; which is grounded. Although theinvention is described in connection with an alternating current supplythat has one side grounded in accordance with the standard practice fornormal residential and commercial power distribution systems, theballast apparatus 10 of the present invention can be operated fromsupply sources which are not grounded.

During operation, the cathodes 16, 17 of fluorescent lamp L arecontinuously supplied with cathode heating current by the cathodeheating windings H H which are closely coupled with the primary windingP and connected in circuit with the cathodes 16, 17 by leads 14, 41 and15, 42, respectively. The high potential end of the secondary winding Sis connected with lamp L by the circuit means which includes the outputlead 14. The low potential end of the secondary winding S is connectedwith lamp L by circuit means which includes the capacitor 13 and outputlead 15.

In FIG. 3, -I have illustrated a ballast apparatus 54) suitable foroperating a pair of fluorescent lamp L L capacitively coupled with aconductive plate or fixture 48 connected to ground 49. The ballastapparatus 50 includes the ballast case 51 shown schematically by thedashed rectangle, a high reactance ballast autotransformer 55, a powerfactor capacitor 56 and a starting capacitor 58 having a container 57,and output leads 59, 66.

The high reactance ballast transformer 55 includes a primary winding P asecondary winding S inductively coupled therewith on magnetic core 61,cathode heating windings H H H and magnetic shunts 62. A pair of inputterminal leads 63, 64 are connected across primary winding P and areprovided for connection to a suitable alternating current supply shownschematically by the dashed lines 65, 66, the low potential side of thepower supply line 65 being identified by the ground connection 52.Cathode heating winding H is connected in circuit with the cathodes 67,68 by leads 69, 7t) and cathode heating windings H H are connected incircuit with cathodes 71, by leads 613, '72 and 59, 73, 74,respectively. Cathode heating winding H is an extension winding ofprimary winding P and cathode heating windings H H are tightly coupledwith the primary winding P and may, if desired, be wound directly overthe primary winding P The reactive impedance between capacitors 56, 58and container 57 and the outer foils of capacitors 56, 58 is representedschematically by a capacitor 76 and connections 77, 78 shown in dashedlines. Thus, in the exemplification of the invention shown in FIG. 3,the starting capacitor 53 and the power factor capacitor 56 arepreferably contained within the same metal container 57, and thecontainer 57 is connected by lead 83 to the ballast case 51, which isconnected to a ground 47.

As shown in FIG. 4, capacitors 56, 58 are contained in a singlecontainer 57 provided with three terminals 80, 81, 82. The capacitorcontainer 57 is connected in electrical circuit with the ballast case 51by lead 83, which is attached to the ballast case 51 by solder at oneend and at the other end is connected to an eyelet 84. When cover plate85 of the ballast case is attached, the end of lead 83 at the eyelet 84is brought in good electrical contact with the ballast case 51.

Continuing with the description of the components of the ballastapparatus Ell, as they are shown in MG. 4, it will be seen that cathodeheating windings H H2, H and the primary winding P are included in coilassembly 85 mounted on a central winding leg 86. Secondary winding S isincluded in coil assembly 87 arranged on winding leg 86 adjacent to thecoil assembly 81*? and separated therefrom by shunts 62. The shunts 62provide a leakage path in the magnetic core 61 between the primarywinding P and the secondary winding S It will be noted that the magneticcore 61 has a pair of yoke sections 88, 39 which are held in as sembledrelation with the central winding leg 86 by clamping elements $4), 91 sothat a closed magnetic circuit is formed.

The capacitors employed in the ballast apparatus of the invention areconventional static capacitors having liquid or solid dielectrics and acapacitor roll with interleaved sheets of paper and metallic foil, theroll and the dielectric being sealed in a metal container. Since themetal container is separated from the outer metallic foil by thedielectric within the container, a capacitance exists between thecontainer and the outer metallic foil of the capacitor roll. The amountof this capacitance is a function of the area of the two surfaces, thespacing between the surfaces and the properties of the dielectric. Ihave discovered that the capacitance between the outer foil and themetal container is of sulficient magnitude in static capacitors normallyused in ballasts and this capacitance can be eifectively utilized in thestarting aid circuit by connecting the container to ground.

Referring now to FIG. 5, I have illustrated a conventional capacitorassembly 93 constructed in the usual manner. As is shown in FIG. 5, theassembly 93 is constructed of a capacitor roll 94 comprised of metallicfoils 95, 96, such as aluminum, in which metallic foils are interleavedwith sheets of paper 97, 98 to form foil layers 95, 96 separatedsubstantially only by the paper layers.

As shown schematically in FIG. 1, the upper and lower plates of thecapacitor correspond to the foil layers 95, 96, respectively. Tap straps99, 160 are brought out from the foil layers d5, 96 and connected to theouter terminals 101, 102. The wound assembly of foil layers 95, 96 andpaper dielectric spacers 97, 98 are placed in a metal container 163having a cover 1% arranged thereon so as to hermetically seal thecapacitor roll 94 and dielectric material 195. Because of the spacingwhich necessarily exists between the outer foil layer 96 and capacitorcontainer 103, the capacitance exists between these two metallicsurfaces since they are separated by dielectric material M5. Aspreviously mentioned, the amount of capacitance depends upon the area ofthe surfaces, the spacing and the type of dielectric material used. Inaccordance with the invention, this capacitance is utilized to solelyprovide the impedance that is required in the starting aid circuit inFIGS. 1 and 3.

The operation of the circuit shown in FIG. 1 will now be more fullyexplained. When a voltage is applied to the input terminal leads 21, 22of primary winding P, a voltage will be induced in the secondary windingS as determined by the respective turns ratio of the primary winding Pand secondary winding S. The voltage across the secondary winding S isapplied across lamp L by means of the output leads 14, connected incircuit thereto. Further, the cathodes 16 and 17 are simultaneouslysupplied a heating current by cathode heating windings H H respectively.Also, the auxiliary starting aid circuit causes a potential to beapplied in the immediate vicinity of cathode 16. The current flow in theauxiliary starting aid circuit follows a path from the cathode 16 to thecapacitively coupled conductive plate 13, ground 33, lead 31, capacitorcontainer 9, to secondary winding S, output lead 14 and to cathode 16.Thus, the lead 31 connected to capacitor container 9 solely provides acurrent path for the auxiliary starting aid current to the ballastapparatus. Due to the relatively high impedance presented by thecapacitive reactance between the capacitor container 9 and the outerfoil of the capacitor 13 and the high capacitive reactance between lampL and the conductive plate 18, only an insignificant current in theorder of a few microamperes will flow in this circuit. However, thiscurrent is sulficient to substantially increase the ionization of thegas in the vicinity of the cathode 16 and in conjunction with thevoltage applied by the secondary winding S at the output leads 14, 15causes lamp L to start.

When the lamp has started, the starting aid circuit is substantiallyineffective in the operating circuit and any current flow in thiscircuit is insignificantly small as compared with the current flowingthrough the lamp L.

In the operation of the ballast apparatus 50 shown in FIG. 3, inputterminal leads 63, 64 are connected across supply lines 65, 66 energizedfrom a suitable supply of alternating current such as a 120 volt, 60cycle commercial supply. Voltages are immediately induced in the cathodeheating windings H H H and a cathode heating current is supplied to thecathodes 67, 68, 71, of lamps L and L Also, the open circuit voltagedeveloped across the primary winding P and the secondary winding S ofthe ballast transformer 55 is applied across lamp L the turns ratio ofthe transformer 55 being such that the open circuit voltage is ofsufiicient magnitude to initially start lamp L At the same time, theauxiliary starting aid circuit applies the voltages across primarywinding P and secondary winding S to cathode 71 of lamp L which is incapacitive relation with the conductive plate or fixture. A returnground with the conductive plate 48 is completed through ground 49 toeither the ground 47 to which capacitor container 57 is connected or theground of the low potential line 65.

After lamp L has started, the voltage across the starting capacitor 58is applied across lamp L Lamp L also being in close proximity to theconductive plate 48 has an ionization potential applied to cathode 67 bythe auxiliary starting aid circuit. The gas in the vicinity of thecathode 67 will ionize causing lamp L to become conductive and the opencircuit voltage between cathodes 67, '75 causes a breakdown of the gascontained within lamp L thereby igniting lamp L The starting capacitor58 has sulficient impedance so that no appreciable operating currentwill flow through it when both lamps L and L are ignited. Lamps L and Lare operated in a series circuit relationship across the primary windingP and the secondary winding S of the ballast transformer 55. After thelamps L and L are ignited, only a negligible amount of current will flowfrom the lamp cathodes to the conducting fixture because of the highimpedance of the capacitive coupling between lamps L L and theconductive plate 48.

In order to demonstrate the advantages of the present invention, theballast apparatus Stl shown in FIG. 3 was constructed and tested byoperating a pair of 40 watt fluorescent lamps from a volt, 60 cyclealternating current supply. The high reactance ballast transformer 55was designed to provide a minimum open circuit voltage of 280 voltsacross the output leads 59 and 60. A power factor capacitor 56 having arating of 4 microfarads at 300 volts AC. and a starting capacitor 58having a rating of .05 microfarad was used. The capacitor container 57was grounded to the ballast case 51.

During the measurements of the starting aid potential, the primaryoperating voltage was maintained at 108 volts or at minus 10 percent ofthe rated operating voltage in accordance with standard procedure. Thestarting aid voltage measurements were taken with a Rawson peakrectifier and a Rawson electrostatic voltmeter. The starting aidpotential was measured by reading the voltage between the ballast case51 and the output lead 60. For the circuit shown in FIG. 3, the startingaid voltage or potential between cathode '71 and the ballast case 51 wasfound to be approximately 360 volts when the conductive plate or fixture48 was not grounded.

By way of comparison, similar starting aid voltage measurements weretaken for an identical ballast circuit as shown in FIG. 3 wherein aconventional grounding resistor was connected in circuit with the lowpotential end of the primary P, and the ballast case 51. With a startingresistor and capacitor container in the circuit grounded, the startingaid voltage corresponding to a voltage of 108 volts across the primarywinding was found to be 280 volts. Also, with the starting aid resistorinstalled but with the capacitor container ungrounded, it was determinedthat the measured starting aid voltage was approximately 278 volts.Thus, it will be seen that by grounding the capacitor container and byeiminating hte grounding resistor an increase of approximately 28.5percent is obtained in the starting aid potential.

Where the fixture 4-8 was grounded as shown in FIG. 3, the starting aidvoltage was measured at 304 volts with the capacitor container 51grounded and without a starting aid resistor. By way of comparison, theballast apparatus with a starting aid resistor connected to the lowpotential end of the primary P, and with the capacitor containerungrounded was tested. The starting aid voltage was measured at 260volts. Further, with the starting aid resistor in the circuit and thecapacitor container grounded, the starting aid voltage was measured at262 volts.

Preferably, it was found that the capacitance between the capacitorcontainer 57 and the outer foil of the capacitor should not be less than880 picofarads. It was found that when the ballast apparatus 59 shown inFIG. 3 was operated from an ungrounded power supply and with thecapacitor container 57 grounded that the auxiliary starting aid voltagebegan to decrease below 880 picofarads. The capacitor container 57 ofcapacitors 56, 5% used in the circuit provided a capacitance between thecontainer 57 and the outer foil of capacitors 56, 58' of approximately1700 picofarads. However, where the circuit was operated with a normallygrounded supply, it was noted that variations in the capacitance betweenthe outer foil and container 57 did not have an appreciable effect onthe starting aid potential.

From the foregoing description, it will be apparent that the auxiliarystarting circuit arrangement of the present invention not only providesa significant improvement in the auxiliary starting aid voltage, butalso eliminates the need for a grounding resistor.

It will be understood that while I have illustrated my invention byspecific embodiments thereof, the invention has general applicability toballast circuits which utilize an auxiliary starting circuit to aid inthe starting of the fluorescent lamps. Thus, the invention may beemployed in ballast circuits used to start and operate rapid start andinstant start lamps. It will also be apparent to those skilled in theart that the auxiliary starting circuit arrangement in accordance wihtthe invention can be employed in many other ballast circuitconfigurations other than those which have been illustrated herein byway of exemplification of the invention. While the present invention hasbeen described by reference to specific exemplifications thereof, it isto be understood that modifications may be made by those skilled in theart without actually departing from the invention. It is, therefore,intended in the appended claims to cover all such equivalent variationsthat fall within the true spirit and scope of the invention.

What I claim as new and; desire to secure by Letters Patent of theUnited States is:

1. A ballast apparatus for starting and operating at least onefluorescent lamp disposed in a capacitive relation with a conductivefixture, said apparatus comprising a high reactance transformer having aprimary winding and a secondary winding inductively coupled therewith Ona magnetic core, a pair of input terminal leads connected across saidprimary winding, a circuit means including a pair of output leads forapplying the output of said transformer across said lamp, a capacitorserially connected with said secondary winding to cause a leadingcurrent to iiow therethrough, a conductive ballast case, said highreactance transformer and capacitor being disposed in said ballast case,said capacitor including a capacitor roll having electrodes ofinterleaved foil layers and a conductive container for housing saidcapacitor and disposed in capacitive relation with the outer foil layerand circuit means for connecting said container in electrical circuitrelationship with said ballast case, the capacitance between saidcontainer and said outer foil layer providing sufiicient impedanceduring operation to prevent any significant current flow from theapparatus to said ballast case and said circuit means for connectingsaid container providing the only return path within said ballast casefor the auxiliary starting aid current.

2. The ballast apparatus set forth in claim 1 wherein said secondarywinding is connected in isolated transformer relationship with saidprimary winding.

3. Ballast apparatus for starting and operating a gas eons dischargelamp from a source of alternating current, said lamp being mounted in aconductive fixture and disposed in capacitive relationship therewith,said apparatus comprising: a high reactance transformer having a.primary winding and a secondary winding inductively coupled therewith ona magnetic core and a pair of input leads for connection across thealternating current source; a power factor capacitor connected in seriescircuit relationship with said secondary winding to cause a leadingcurrent to flow therethrough, a ballast case, said power factorcapacitor and said high reactance transformer being housed in saidballast case, said capacitor including a capacitor roll and a metalliccontainer providing an enclosure for at least said power factorcapacitor, circuit means connecting said container in electrical circuitrelationship with the ballast case, said circuit means providing theonly return path for the auxiliary starting aid current when saidalternating current source is not grounded, the capacitive reactancebetween said capacitor roll and said container providing sufficientimpedance to prevent any significant current flow from the apparatus tothe ballast case thereby eliminating the need for a grounding resistor,and circuit means including electrical leads for connection across saidlamp to apply the output of said high reactance transformer across saidlamp.

4. A ballast apparatus for starting and operating at least onefluorescent lamp from an alternating current supply, said lamp beingdisposed in a capacitive relation with a conductive plate, saidapparatus comprising: a high reactance transformer having a primarywinding and a secondary winding inductively coupled therewith on amagnetic core, a pair of input terminal leads connected across theprimary winding for connection to the alternating current supply, acapacitor connected in series circuit relationship with said secondarywinding to cause a leading current to flow therethrough, a ballast casefor housing said apparatus, said capacitor having a metallic containerand a capacitor roll, said container being spaced from said roll anddisposed in capacitive relation therewith and circuit means connectingsaid metallic container in electrical circuit relation with said ballastcase and forming a low potential connection in the starting aid circuit,said capacitive reactance between said capacitor container and said rollproviding sufficient reactive impedance to prevent any significantcurrent flow to said ballast case, and said circuit means providing theonly return path for the auxiliary starting aid current when saidalternating current supply is not effectively grounded.

5. A ballast apparatus for starting and operating a gaseous dischargelamp from an alternating current supply, said lamp being mounted in aconductive fixture and disposed in capacitive relationship therewith,said apparatus comprising: a ballast transformer having a primarywinding and a secondary winding inductively coupled therewith on amagnetic core, said secondary winding being in isolated transformerrelationship with said primary winding, a pair of input leads forconnection across the alternating current supply, said primary windingbeing connected across said input terminal leads, a capacitor connectedin series circuit relationship with said secondary winding to cause aleading current to flow thereto, a ballast case for housing saidapparatus, said capacitor having a metallic container and a capacitorroll formed of foil layers and dielectric layers, said roll beingdisposed in said metallic container, said metallic container beingspaced from said roll and capacitively coupled with the outer foil layerof said roll and circuit means connecting said metallic container inelectric circuit relation with said ballast case in order to provide agrounded connection for the ballast apparatus in a starting aid circuit,said capacitive reactance between said capacitor container and saidouter foil layer providing suflicient reactive impedance to prevent anysignificant current flow from said ballast transformer to said ballastcase and said circuit means providing the only return path for theauxiliary starting aid current from the conductive fixture.

6. A ballast apparatus for starting and operating a pair of fluorescentlamps from an alternating current supply, said lamps being disposed incapacitive relation with a conductive plate so that .an auxiliarystarting aid current can flow thereto, said apparatus comprising: a highreactance transformer having a primary winding and a secondary windinginductively coupled therewith on a magnetic core, a pair of inputterminal leads connected across the primary winding for connection tothe alternating current supply, a power factor capacitor connected inseries circuit relationship with said secondary winding to cause aleading current to flow therethrough, a starting capacitor, circuitmeans including electrical leads for connecting the output of said highreactance transformer across said fluorescent lamps and for connectingsaid starting capacitor across one of said lamps, said power factorcapacitor and said starting capacitor being enclosed in a metalliccontainer and having a capacitor roll formed of interleaved foil layersand dielectric layers disposed in said container, and grounding circuitmeans connecting said metallic container in electrical circuit relationwith said ballast case in order to provide a grounded connection for theballast apparatus in the auxiliary starting aid circuit, said capacitivereactance between said metallic container and the outer foil layer ofsaid roll providing suflicient impedance to prevent any significantcurrent flow from said ballast apparatus to said ballast case and saidgrounding circuit means providing the only return path for the auxiliarystarting aid current from the conductive plate to the ballast apparatus.

7. A ballast apparatus for starting and operating a pair of seriallyconnected fluorescent lamps from an alternating current supply, saidlamps being disposed in capacitive relation with a conductive plate sothat an auxiliary starting aid current can flow therethrough, saidapparatus comprising: a high reactance transformer having a primarywinding and a secondary winding inductively coupled therewith on amagnetic core, a pair of input terminal leads for connection to thealternating current source, said primary winding being connected acrosssaid input terminal leads, a capacitor connected in series circuitrelationship with said secondary winding to provide a leading currenttherethrough, a ballast case for housing said apparatus, a startingcapacitor, circuit means including electrical leads for connecting theoutput of said high reactance transformer across said serially connectedlamps and for connecting said starting capacitor across one of saidlamps, at least one of said capacitors having a metallic container and acapacitor roll having interleaved foil layers and dielectric layersdisposed therein, the outer foil layer of said capacitor roll beingspaced from said metallic container and in capacitive relationtherewith, grounding circuit means connecting said metallic container inelectrical circuit relation with said ballast case to provide a groundedconnection for the ballast apparatus, the capacitive reactance betweensaid capacitor container and the outer foil layer providing suflicientimpedance to prevent any significant current flow from the highreactance transformer to said ballast case during operation and saidgrounding circuit means providing the only return path for auxiliarystarting aid current from said conductive plate.

8. A fluorescent lamp lighting system comprising at least onefluorescent lamp, a conductive plate, said lamp being disposed incapacitive relation with said conductive plate so that an auxiliarystarting aid current can flow thereto, a high reactance transformerhaving a primary and a secondary winding inductively coupled therewithon a magnetic core, a pair of input terminal leads connected across saidprimary winding, circuit means including electrical leads for connectingthe output of said high reactance transformer across said lamp, acapacitor serially connected with said secondary winding to causeleading current to flow in said secondary winding, said capacitorincluding a capacitor roll having interleaved foil layers and dielectriclayers and a metallic container disposed in capacitive relation with atleast the outer foil layer of said roll, a ballast case for housing saidapparatus, grounding circuit means connecting said capacitor containerin electrical circuit relation with a ballast case for providing agrounded connection to form a starting aid circuit with said conductiveplate, said capacitive reactance between said outer foil layer of saidcapacitor roll and said container providing suflicient impedance toprevent any significant current flow from said high reactancetransformer to said ballast case during operation, and said groundingcircuit means providing the only return path for the auxiliary startingaid current from said conductive plate to said ballast apparatus.

9. A fluorescent lamp lighting system comprising a pair of fluorescentlamps, a conductive plate, said lamps being disposed in capacitiverelation with said conductive plate so that a starting aid current canflow thereto, said conductive plate being grounded, a high reactancetransformer having a primary winding and a secondary winding inductivelycoupled therewith on a magnetic core, a pair of input terminal leadsconnected across said primary winding and provided for connection acrossan alternating current supply, a capacitor connected in series circuitrelationship with said secondary winding to cause a leading current toflow therethrough, a starting capacitor, a ballast case for housing theballast apparatus, circuit means including electrical leads for applyingat least the voltage across said secondary winding across said lamps andfor connecting said starting capacitor across one of said lamps, saidstarting capacitor and power factor capacitor having a metalliccontainer and a capacitor roll formed of interleaved foil layers anddielectric layers, the outer foil layer of said capacitor roll beingdisposed in capacitive relation with said metallic container, thereactive capacitance between said container and said capacitor rollproviding sufiicient impedance during operation to prevent anysignificant current flow from the high reactance transformer to saidballast case, grounding circuit means connecting said metallic containerto said ballast case for providing a grounded connection, said groundingcircuit means providing the only return path for the auxiliary startingaid current when said power supply is not grounded.

10. Aballast apparatus for starting and operating from an alternatingcurrent supply at least one gaseous discharge lamp disposed in acapacitive relation with a grounded conductive plate, said apparatuscomprising a pair of input terminal leads for connection With thealternating current supply, a ballast means, a capacitor, said capacitorhaving a capacitor roll and a conductive container disposed incapacitive relation with said roll to provide a capacitancetherebetWeen, circuit means including electrical leads for connectionWith said lamp, said circuit means connecting said input terminal leads,said ballast means and said capacitor in circuit with said electricalleads for connection with said lamps so that a leading current issupplied to said lamp and a current limiting impedance is provided forsaid lamp, a conductive ballast case for housing said apparatus andarranged for connection to said conductive plate, and circuit meansconnecting said container in electrical circuit with said ballast case,said capacitance providing sufficient impedance during operation toprevent any significant current fiow from the apparatus to said ballastcase and said last mentioned circuit means providing the sole pathwithin said ballast case for auxiliary starting aid current to saidconductive plate and lamp.

References Cited in the file of this patent UNITED STATES PATENTS

1. A BALLAST APPARATUS FOR STARTING AND OPERATING AT LEAST ONEFLUORESCENT LAMP DISPOSED IN A CAPACITIVE RELATION WITH A CONDUCTIVEFIXTURE, SAID APPARATUS COMPRISING A HIGH REACTANCE TRANSFORMER HAVING APRIMARY WINDING ANMD A SECONDARY WINDING INDUCTIVELY COUPLED THEREWITHON A MAGNETIC CORE, A PAIR OF INPUT TERMINAL LEADS CONNECTED ACROSS SAIDPRIMARY WINDING, A CIRCUIT MEANS INCLUDING A PAIR OF OUTPUT LEADS FORAPPLYING THE OUTPUT OF SAID TRANSFORMER ACROSS SAID LAMP, A CAPACITORSERIALLY CONNECTED WITH SAID SECONDARY WINDING TO CASE A LEADING CURRENTTO FLOW THERETHROUGH, A CONDUCTIVE BALLAST CASE, SAID HIGH REACTANCETRANSFORMER AND CAPACITOR BEING DISPOSED IN SAID BALLAST CASE, SAIDCAPACITOR INCLUDING A CAPACITOR ROLL HAVING ELECTRODES OF INTERLEAVEDFOIL LAYERS AND A CONDUCTIVE CONTAINER FOR HOUSING SAID CAPACITOR ANDDISPOSED IN CAPACITIVE RELATION WITH THE OUTER FOIL LAYER AND CIRCUITMEANS FOR CONNECTING SAID CONTAINER IN ELEC-